Hi Joe,Remember when I said (after the other replies) that it may or may "not" help? That was the reason I responded in the first place is because "grounding" is not about spark lengths, it's about component protection. For spark length increases I mentioned the gap as did others and also more power needed. These are still the two main adjustments you can make to your coil to gain spark length. The gap is always #1 on the list of things to do. Carriage bolts have been used by everyone at some point (including myself), but there is a time when you must simply build a smart gap that is smart for Tesla coil systems.
When considering a static gap, it's important to understand "why" a tube is better than a solid stock of anything else. The tube has a great deal of surface area (both inside the tube and outside the tube). This area allows heat to be radiated away from the initial path of high current contact of the spark as well as the build up of heat throughout the tube. A bolt or even a cylindrical tube which is solid, only has the outer surface to dissipate heat. The thicker the solid stock, the slower it will rise to temp, but, even thick solid stock electrodes heat up rather quickly and then performance begins to diminish due to the poor ability to radiate heat away. Tubes however, have the ability to radiate heat away when air is blown through them and across them. Thin walled tubes are actually better for this as opposed to thick walled tubes. Consider a 1" diameter sphere made of copper. Heat it up to 300 degreesF. Then do the same with a 1mm sphere. The 1mm sphere will heat up to temp faster because it's mass is smaller. But, it will also cool faster. Thin walled tubes act the same way. They heat up quick but they also cool down quick, so they are easier to maintain a specific temperature without a wide variation. They are more responsive to air flow and this is a key aspect.
Both hyperbaric and TCBOR cylinder spark gaps use tubes. Tubes do very well. Tubes on a flat slab are not wonderful simply due to how the air is forced across the tubes. Ideally, you want cool air from the outside to be drawn in across both the outer and inner surfaces equally for all the tubes (that's hard to do on a slab). The TCBOR gap allows this very feature if built correctly. The hyperbaric gap also pushes air inside and outside the tubes. The hyperbaric gap has the added advantage that there are only 2 tubes. This is both a mechanical and electrical advantage.
Although air might help your carriage bolts (barely), a new gap and doubling the power is what will help your coil perform to the potential it is capable of. You can certainly skip around this and look at other avenues, but none of those avenues will lead you to greater spark lengths.
Take care, Bart jocatch wrote:
Hello. I am somewhat disappointed at the moment. Tonight I got to fire up the coil now that the secondary and nst are grounded to earth and I have a boxer fan blowing on the gap. I am only getting 12" sparks to ground using my 14 turn prin/1400 second with 12kv/30ma nst, .0125uf mmc and 4"x17" toriod. The Q of the circuit must be pretty low as moving the tap from 14 to 15 turns make almost no difference. Adjusting the gap wider apart makes a little difference but going too wide and I start getting flash over somewhere near the nst and some spark jumps from the pri to sec. As I said before, the pri is too close to the sec form, almost flush up against it. If I try to move the pri up (right now it is at least 1" below the secondary) I get spark shorts between the two.So I plan to increase the pri diameter and then raise the pri coil and see if that helps. I am still thinking about getting a blower fan for the gap.Joe C. ----- Original Message ----- From: "bartb" <bartb@xxxxxxxxxxxxxxxx> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Sent: Friday, April 17, 2009 10:18 PM Subject: Re: [TCML] Questions on groundingHi Joe,I don't think your over-coupled, but it would be normal to start the primary turn 1.25" from the secondary outer diameter (due to the 12kV supply and your coil) , then raise the primary to 1.5" above the bottom secondary turn as measured from the center of the primary. This will put coupling at 0.13 for your particular coil. Looks to be about 13.9 turns on the tap if that is done.For coupling, well, don't ask for a calc. Use Javatc or other program for something like that.Take care, Bart jocatch wrote:Hello Christopher (and everyone else who responded),I haven't had time yet to fire up the coil at night since I grounded the secondary and nst case to earth ground. Will do tomorrow night. I also relocated my spark gap so I can blow air on it. Right now I am still using the cartridge bolts but I got a 120v 100 cfm boxer fan about 2" away blowing air on it. If it improves the output, I'll look for a blower fan that really cranks and see if that works.Of course I need to be more exact in my breakout measurements so I am going to mount a grounded wire on a pole and set on a tripod so I can accurate measure the spark length to gauge improvements.I am also thinking I may be over coupled. The inside of the primary is almost flush up against the secondary form. The primary is about 1" lower than the bottom of the secondary coil. If I try to raise the primary so it is even with the secondary winding, I get sparks. So I may rewind the primary out another inch or two.Thanks for everyone's input so far. Joe----- Original Message ----- From: "Christopher Karr" <chriskarr4@xxxxxxxxxxx>To: "Tesla Pupman List" <tesla@xxxxxxxxxx> Sent: Wednesday, April 15, 2009 3:50 PM Subject: RE: [TCML] Questions on grounding Hello Joe,The reason that a fan on the spark gap helps improve output of a Tesla coil is that it helps to extinguish the arc and blow out the ions. When the ions are all gone, the gap takes a higher voltage to make it break down, which means that there's more 'bang energy', resulting in more energy transferred to the secondary coil and that means larger streamers on the output.ChristopherFrom: jocatch@xxxxxxxxxxx To: tesla@xxxxxxxxxx Subject: Re: [TCML] Questions on grounding Date: Wed, 15 Apr 2009 14:01:07 -0400 CC: Hello to everyone who has responded so far. Thank you!Today I went and got a 4' ground rod and banged it into the ground and ran a wire to the secondary coil and nst case. I used a 4' rod because my ground here has lots of rocks and I have never been able to go more than about 4' with ground rods. As you can see from my photos that the coil is on my rear deck, there is no concrete floor. The wire from the coil to the rod is less than 20' long. Tonight after dark I will power it up and see if it helped. I will also connect the ground wire to the end of a pole and see how long of aspark I can get.Regarding my spark gap, I always go for the easiest, simplest solution as I am not that mechanically inclined. I do have some 12v computer fans I was thinking about placing near the gap to see if it helps. But I wanted to trythe grounding, tuning and adjusting the gap width before adding a fan.Besides, I have no place right now to add the fan on the base; I will have to move the gap to somewhere where there is more room. Regarding a 'sucker'gap, I am not sure what that is, I will have to research that. Joe ----- Original Message ----- From: "Lau, Gary" <Gary.Lau@xxxxxx> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Sent: Wednesday, April 15, 2009 10:36 AM Subject: RE: [TCML] Questions on grounding Hi Joe,When you say that "Right now, nothing is grounded to earth or electrical ground", this is REALLY bad! The secondary base needs a ground connection. If there is not a good, direct ground connection, the RF current will travel through your hot & neutral wires and wreak havoc with household appliances.I agree with Bart's reply - that the secondary base is typically connected to the NST case, and that this case connection should go to a dedicated RF ground, not the mains ground. For low powered coils, the mains ground isoften used, but the definition of "low" is subjective.Regarding the sparks discharging all around the toroid, this may be due to having a ragged surface on the toroid, so smoothing it out may help. If the toroid is simply too small for the power level you're running at, no amount of surface prep is going to help, but yours appears to be reasonable insize. Looking at your web site, I think the weak link in your coil is the 2carriage bolt spark gap. It needs forced air flow directly through the arc (more than just a gentle breeze from a fan), and should be designed to arc not at just a single point as yours will. I recommend using a sucker gap,as it's easy to build and works very well. Regards, Gary Lau MA, USA-----Original Message----- From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of jocatch Sent: Tuesday, April 14, 2009 9:35 AM To: tesla@xxxxxxxxxx Subject: [TCML] Questions on groundingHello. I have built my first coil using standard parts and dimensions andhave fired itup and so far I am producing sparks but only about 12" long. I am using a12KV nst with .0125uf mmf, 13 turns of copper tubing as primary and 20" of #28 magnet wire on a 4" form with aluminum cloths dryer ducting for the toroidMy questions concerning grounding. I have read alot about discharge sparklengthbut not much regarding how to measure it. Above I said 12" discharge sparklength,that was to a key ring held at the end of a boom stick handle. Should themetalobject that I am drawing the spark to be grounded? To earth ground? Rightnownothing is grounded to earth or electrical ground. The bottom side of thesecondarycoil is connected to the metal case of the nst. Should the secondary coiland nst be grounded to earth ground?Lastly, the aluminum toroid is discharging all around its circumference. Iknow thefewer discharge points on the top load, the bigger the discharge lengthwill be. If Itape the toroid with aluminum tape to produce a smoother surface, will ithelp?I have a web page showing photos of my first tesla coil before I recentlyupdated itto copper tubing and new toriod. The web page shows the old primary wirecoil and old topload. I will post new pictures of the update soon. http://www.joecool.org/joe_s_tesla_coil.htm Thanks for your help. joe_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_________________________________________________________________ Rediscover Hotmail®: Get e-mail storage that grows with you.http://windowslive.com/RediscoverHotmail?ocid=TXT_TAGLM_WL_HM_Rediscover_Storage1_042009_______________________________________________Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla